The present invention relates generally to methods for manufacturing metals, metal alloys, and metal oxides and more particularly to a method for manufacturing metals, metal alloys, and metal oxides by electrodeposition of polymetallic complexes.
The utility of metals, metal alloys, and metal oxides in, for example, the semiconductor industry, the magnetic recording materials industry, and the chemical catalyst industry, is well established. For instance, compositionally uniform mixed metals and alloys are extensively used as nanostructural materials, thin films, and catalysts. Certain nickel-containing alloys are used for oxidative protection of very fine ferromagnetic iron particles in various types of magnetic recording media. Fine metal and metal oxide powders are strategically important materials and are the bedrock of industry. Morphologically uniform mixed-metal and alloy powders are also of intense interest for their utility in selective catalysis. Accordingly, better ways for making metals, metal alloys, and metal oxides are constantly being sought.
Many different techniques presently exist for producing metals, metal alloys, and metal oxides. Examples of conventional techniques include the thermal decomposition of solid or gaseous metallic compounds and the reduction of metal ions in solution. Unfortunately, only in rare cases can these methods be used to obtain highly dispersed mixed-metal deposits. In fact, the electrodeposition of many desirable alloys from solutions containing separate sources of different metals (e.g. Cu from CuCl.sub.2 and Ni from NiCl.sub.2) is particularly difficult since each metal is typically reduced at a different potential and at a different rate for a fixed potential. Additionally, as a general rule, these conventional methods of synthesis typically offer very little control over the composition, morphology, or catalytic properties of the synthesized products. Moreover, these methods rarely result in the formation of single grains of metallic powders that are smaller than about 1 micron in diameter as aggregates of many contiguous crystallites readily form.
In U.S. Pat. No. 4,933,003, which issued to Marzik et al. on Jun. 12, 1990, and which is incorporated herein by reference, there is disclosed a method for forming a single-phase, homogeneous and high surface area metal alloy. The method described therein comprises the following two-step process: (1) formation by a transmetalation reaction of a heteropolymetallic complex containing the desired metals (See, e.g., El-Toukhy et al., J. Amer. Chem. Soc., Vol. 106, 4596 (1984); Davies et al., Inorg. Chem., Vol. 25, 2373 (1986); Davies et al., Comm. Inorg. Chem., Vol. 8, 203 (1989); Abu-Raqabah et al., Inorg. Chem., Vol. 28, 1156 (1989); Al-Shehri et al., Inorg. Chem., Vol. 29, 1198 (1990); and Caulton et al., Polyhedron, Vol. 9, 2319 (1990), all of which are incorporated herein by reference, for information on the formation of polymetallic complexes by transmetalation reactions.); and (2) reduction of the heteropolymetallic complex to a single-phase alloy by heating the complex in hydrogen gas to a temperature equal to or greater than its decomposition temperature for a sufficient period of time.
In U.S. Pat. No. 5,061,313, which issued to Davies et al. on Oct. 29, 1991, and which is incorporated herein by reference, there is disclosed another method for forming a single-phase, homogeneous and high surface area metal alloy. The method described therein comprises the following two-step process: (1) formation by a transmetalation reaction of a heteropolymetallic complex containing the desired metals; and (2) reduction of the heteropolymetallic complex a single-phase alloy by heating the heteropolymetallic complex for a sufficient period of time in an inert atmosphere to a temperature at which reductive decomposition occurs.
Additional studies have disclosed that thermoloysis of the heteropolymetallic complex (.mu..sub.4 -O)N.sub.4 CoNiCuZnCl.sub.6 in O.sub.2 at approximately 220 degrees Celsius gives highly dispersed mixtures of Co.sub.3 O.sub.4, NiO, CuO and ZnO. The formation of separate oxides rather than complex oxide phases is thought to be the result of the intervention of a molten precursor state.
In Inorganica Chimica Acta, Vol. 182, pp. 213-220 (1991), El-Sayed et al. disclose the results of routine cyclic voltammetric studies performed at a Pt electrode in 0.1M tetrabutyl ammonium perchlorate-methylene chloride (TBAP-MC) with polymetallic complexes of the formula (.mu.-O) (N,py).sub.4 Cu.sub.4-x Ni.sub.x Cl.sub.6, wherein N is N,N-diethylnicotinamide and py is pyridine. These redox behavior studies suggested that polymetallic complexes of the formula (.mu.-O) (N,py).sub.4 Cu.sub.4-x Ni.sub.x Cl.sub.6 are electrochemically inactive, i.e., they do not produce an electrochemical response, a deposition of metal, or result in the reduction/oxidation of the polymetallic complex. El-Sayed et al. also disclose analogous studies performed under the same conditions with polymetallic complexes of the formula (.mu.-Y)N.sub.4 Cu.sub.4-x (OH).sub.2 Ni.sub.x Cl.sub.4.3H.sub.2 O (where Y=3,4,5,6-tetrachlorocatecholate). Although these studies showed some electrochemical activity, i.e., quasi-reversible behavior, with the peak potentials altered by substitution of nickel for copper, the electroactivity found with this latter group of complexes was attributed to the ligands, i.e., the catecholate groups. In no instance was electrodeposition reported or demonstrated by their data.